[Haskell-cafe] Working Generic/Polytypic Haskell extension

Hi all, I would like to teach a small section on polytypism/genericity in the "functional programming using Haskell" course I'm teaching. I won't, though, unless I can assign an actual programming exercise in polytypic programming, however brief. Can anybody recommend a functioning compiler that I can reasonably require the students to use in doing this assignment? I am not up-to-date on the current state of research in this topic in Haskell and hope that some people on the list can help me out. Thanks! - mulhern